This invention relates to a multivibrator circuit having a first and a second current branch each of which comprises a series arrangement of a resistance, a main current path of a main transistor and a controllable current source, wherein the first connection nodes between each main current path and its controllable current source are coupled to each other via a capacitance, and a control electrode of the main transistor, having its main current path inserted in the one current branch, is coupled to a second connection node between the resistance and the main current path of the main transistor in the other current branch, whereby the controllable current sources are oppositewise controlled thereby generating alternately in each of the current branches in a first state a first current and in a second state a second current.
Such a multivibrator circuit is known from JP-Kokai 60-70804, where it is used as a delay element in a FM demodulation circuit.
The controllable current sources in the known delay element are constituted by a long tailed transistor pair, the control electrodes thereof receiving mutually complementary signals to be delayed. The currents supplied by the controllable current sources in both the first and second state depend on the exact values of the input voltages, representing the input signals, on the control electrodes of the long tailed transistor pair. The ratio of these currents determines the delay time attributed to the signals.
It is an object of the invention to provide a multivibrator circuit in which the delay time is exactly determined in dependence on the input signals without the need for feeding the controllable current sources with input signals having accurately determined values. A way of adjusting the delay time in the prior art circuit is to adjust the total current drawn by the controllable current sources. Then the problem arises that the voltage swings across the resistances are changed.
These voltages represent output signals to be fed to the next circuits. Changes therein, induced by the adjustment, could be dealt with by buffers inserted between the multivibrator circuit and the next circuits. However, this increases the number of circuits. It is therefore a further object of the invention to provide a multivibrator circuit having a constant voltage swing across the resistances independent of the adjustment of the total current drawn by the controllable current sources.